In this project we propose to develop, validate, and apply a technique for visualizing function of the sympathetic nervous system in humans by positron emission imaging after systemic intravenous administration of positron-emitting fluoro-dopamine. The project includes several studies designed to interpret clinical PET results in terms of synthesis, release, uptake, and metabolism of the sympathetic neurotransmitter norepinephrine; and to measure alterations in activity of these processes as a function of normal aging. The results in normal volunteers will provide the basis for comparisons with those in patients with clinical pathologic conditions; the patients will be studied under other protocols.